drm/i915/gvt: set the correct default value of CTX STATUS PTR

Fix wrong initial csb read pointer value. This fixes the random
engine timeout issue in guest when guest boots up.

Fixes: 8453d674 ("drm/i915/gvt: vGPU execlist virtualization")
Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Min He <min.he@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/execlist.c

@@ -775,7 +775,8 @@ static void init_vgpu_execlist(struct intel_vgpu *vgpu, int ring_id)
 			_EL_OFFSET_STATUS_PTR);
 
 	ctx_status_ptr.dw = vgpu_vreg(vgpu, ctx_status_ptr_reg);
-	ctx_status_ptr.read_ptr = ctx_status_ptr.write_ptr = 0x7;
+	ctx_status_ptr.read_ptr = 0;
+	ctx_status_ptr.write_ptr = 0x7;
 	vgpu_vreg(vgpu, ctx_status_ptr_reg) = ctx_status_ptr.dw;
 }